1. Field of the Invention
This invention relates to a multiple-color-band light source and, in particular, to such a light source which is especially useful with video projection systems for scrolling such light bands across a single-panel light valve.
2. Description of Related Art
U.S. Pat. No. 5,548,347, which is hereby incorporated by reference, discloses a number of systems in which light from an intense white light source, for example an arc lamp, is collected, and separated using dichroic filters into light bands of the primary colors, i.e. red, green and blue. The color-separated light bands are arrayed adjacently, with each band being narrower in one direction, e.g. the "vertical" direction, and wider in another direction, e.g. the "horizontal" direction. Scanning optics are employed to cause the three bands of light to be imaged onto a light-valve panel. This arrangement proves very effective when utilizing a matrix display panel such as, for example, a liquid crystal display (LCD) panel. Regardless of what type of light-valve panel is utilized, the scanning optics cause the bands of illumination to move across the panel. As each band passes over the "top" of the active area of the panel, a band of light of that color typically leaves the "bottom" of the panel. Accordingly, there is a continual sweep of the three colors across the panel.
Prior to each color band passing over a given row of pixels on the panel, that row will have been addressed with the appropriate brightness information for that color. Each row of the panel is addressed three times for each video field which is to be displayed.
The simultaneous use of a substantial portion of the available red, green and blue light through a single light valve panel provides optical efficiencies comparable to that of three-panel systems employing the same types of light-valve panels. Using only a single panel eliminates the need to mechanically converge different color images, formed on separate panels, and further reduces system cost. Additionally, beam-combining dichroic filters are not needed which leads to further cost savings. The various scanning systems disclosed in U.S. Pat. No. 5,548,347 have many advantages, particularly optical efficiency. The only color-band light source disclosed in detail in that patent, however, is complicated to manufacture and produces color bands which follow light paths of uncompensated different lengths to facets of a rotatable prism and contribute to entendue problems.